Generally, in a gas combustion type driving tool, a gas canister is connected to a combustion chamber by a gas pipeline. During a striking operation, fuel gas filled within the gas canister is jetted and supplied by a predetermined quantity to the combustion chamber in a sealed state. The fuel gas is mixed with air in the combustion chamber to obtain mixed gas. The mixed gas is ignited by an ignition plug and explosively burnt. A striking piston in a striking cylinder is driven by a combustion pressure and a fastener is driven from a nose part provided in a lower part of the tool main body by a driver integrally connected to the striking piston.
In the driving tool main body, a measuring chamber for storing the predetermined quantity of the fuel gas is arranged in a vicinity of an injection port of the fuel gas of the gas canister. In an outlet of the measuring chamber, an injection valve is provided. Ordinarily, the gas jetted from the gas canister is stored in the measuring chamber to shut off the injection port of the fuel gas by the injection valve. During the striking operation, the gas pipeline is opened to the combustion chamber (is shut off relative to the gas canister) by the injection valve interlocking with an operation of a trigger to supply the fuel gas in the measuring chamber to the combustion chamber from the gas pipeline. At this time, the injection valve simultaneously shuts off the gas canister and the measuring chamber so as not to supply the fuel gas in the gas canister to the measuring chamber (see Patent Document 1).    Patent Document 1: JP-B2-2956004
The gas canister to be used has a double structure including an inner vessel filled with the fuel gas and an outer vessel filled with propellant gas whose internal pressure is higher by 2 to 3 atmospheric pressure than an internal pressure of the inner vessel. The inner vessel is pressed by the gas pressure of the propellant gas to jet the fuel gas. In this structure, the pressure of the propellant gas operates when the injection valve closes the gas pipeline to the combustion chamber and opens to the gas canister. During the jet of the fuel, when the injection valve shuts off a part between the measuring chamber and the inner part of the gas canister as described above, the pressure of the propellant gas does not operate. Accordingly, the fuel gas is supplied to the combustion chamber only by a vaporizing pressure of the fuel gas from the measuring chamber.
However, when the vaporizing pressure of the fuel gas is lowered, for instance, when the fuel gas is used under a low temperature environment, it takes much time for the fuel gas in the measuring chamber to enter the combustion chamber or a part of the fuel gas remains in the measuring chamber. Therefore, there is a fear that the fuel gas may not be ignited or cannot be ignited when a predetermined time does not elapse.